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MCQ 1.2 > Alginate > Flashcards

Alginate Flashcards

1
Q

What are 3 synthetic elastomers of impression materials

A

Polysulphides
Silicones
Polyethers

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2
Q

What are the 2 hydrocolloids impression materials

A

Reversible (agar)
Irreversible (alginate)

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3
Q

What are the 4 non elastic impression materials

A

Impression plaster
Impression compound
Zinc/oxide eugenol pastes
Impression waxes

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4
Q

What are the 2 elastic impression material categories

A

Synthetic elastomers
Hydrocolloids

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5
Q

What are 7 requirements of impression materials

A

Short workable time
Non toxic
Easily removed when set
Record anatomy accurately
Dimensionally stable
Palatable taste
Cost efficient

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6
Q

What are 5 properties of irreversible hydrocolloids

A

Based on alginic acid which is derived from marine plants
When mixed with water a reaction occurs where the polymer chains cross link
Main component of alginate powder is in fact fillers to control the consistency
The setting process in alginate is irreversible
It is an endothermic reaction

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7
Q

What are 5 tray properties

A

Rigid
Extension
Retention
Handle position
Sterilisation

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8
Q

What are special impression trays

A

Custom made usually from acrylic provide a uniform gap between the tray and the dental structures being recorded

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9
Q

What are 2 types of impression trays

A

Stock trays plastic or metal
Special trays

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10
Q

What are 5 considerations for choosing an impression tray

A

Anatomy led
Sufficient depth, width and length
Consider the distribution of any teeth remaining
Have enough space for 3mm of alginate (minimum)
Perforations and adhesives

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11
Q

What is the reason for a use of adhesive on the impressions tray

A

Aim is to overcome displacing force during impression removal

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12
Q

What are 3 materials for tray modification/extension

A

Wax
Stick impression compound
Heavy body silicone

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13
Q

How do you mix powder alginate by hand

A

Invert sealed alginate powder container before using measuring spoon to dispense powder into flexible bowl
Use room temperature water at the specific ration to the powder
Spatula used to mix
Paste needs to smooth and free of air bubbles
Spatula then used to load tray

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14
Q

What are the 3 different ways of mixing powder alginate

A

By hand in a flexible bowl
Alginator
Automatic centrifuge mixing machine

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15
Q

Which impression should you take first

A

Lower impression first as a patient is less likely to gag

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16
Q

What is gagging with an impression normally caused by

A

The compression of the soft palate but not necessarily so you may encounter gagging on a lower impression too

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17
Q

How do you load the tray with impression material

A

Spatula used to scoop up mixed impression material and placed into prepared tray
For lower tray may be easier to split mix into two parts
May wish to smooth alginate in tray with wet fingered glove
Any excess impression material may be kept by nurse to check its setting speed - will set faster in mouth due to heat

18
Q

Where should the operator stand when taking a maxillary impression

A

Behind the patient just over the patients shoulder

19
Q

Where should the operator stand when taking a mandibular impression

A

Infront, to the side of the patient

20
Q

What are 5 patient mouth preparations which may be required prior to impression taking

A

Clean mouth
Dentate patients need teeth dried with 3 in 1 syringe
Pre packing of mixed alginate before tray insertion may be beneficial in certain situation such as in sulci
Areas of large undercuts may need waxing out to prevent alginate tearing on removal
Some patients may prefer to have petroleum jelly placed on lips to minimise trauma

21
Q

What can happen if tooth much force is placed on the tray when taking the impression

A

If teeth touch the tray then inadequate alginate thickness results in dental stone can work its way between the tray and alginate during casting, resulting in distortion

22
Q

How do you seat the impression tray

A

Insert into mouth without displacing the loaded alginate
One side of lip retracted with finger or mirror and other side retracted with impression tray
Mild pressure placed in an axial direction
Once seated properly keep fingers on tray to maintain position

23
Q

How should you remove the alginate impression

A

Gentle working of tray buccally to help break seal use of gloved finger or 3 in 1 syringe may be beneficial
Once loosened tray should be removed from patients mouth taking care with patients lips

24
Q

How should you review the impression

A

Under good light
Have all necessary anatomical features been accurately recorded

25
Q

What 4 aspects are you looking for when reviewing an impression

A

Air blows
Tears in material
Perforations through to tray
Soft tissue displacement

26
Q

What does the health and social care act 2012 stated about impression disinfection

A

Dentist has legal obligation to disinfect all material sent to the lab

27
Q

What guidance as written in HTM 01-05 publication from the departments of health state about impression disinfection

A

Rinse impression until visibly clean
Disinfected as per manufacturers instructions
Specific cleaning materials will be in CE-marking instructions
Must be labelled that disinfection has been carried out

28
Q

What is a hydrocolloid

A

A substance which forms a gel in the presence of water

29
Q

What are colloids

A

Mixtures in which one or more substances are dispersed as relatively large solid particles or liquid droplets through a solid, liquid or gas

30
Q

How are reversible impressions reversed

A

As the bonds are easily destroyed by heating
On re heating the gel the material reverts to a sol stage

31
Q

Why is an irreversible impression irreversible

A

Strong cross links are formed and will not revert to the sol form

32
Q

What is a sol form

A

Fluid
Lower viscosity
Random arrangement of poly saccharide chains

33
Q

What is a gel form

A

Thicker
Higher viscosity
Poly saccharide chains become more aligned
Elasticity develops

34
Q

What are 7 constituents of alginate impression materials

A

Alginate salt (sodium alginate)
Calcium salt (calcium sulphate - gypsum)
Trisodium phosphate
Diatomaceous earth (amorphous silica)
Flavourings
Colourings
Chromatic phase indicator

35
Q

What is the bulk constituent of an alginate impression material

A

Diatomaceous earth (amorphous silica)

36
Q

What constituent controls the working time of an alginate impression material

A

Trisodium phosphate

37
Q

What are 5 advantages of alginate

A

Non toxic and non irritant
Good surface detail
Ease of use and mix
Cheap and good shelf life
Setting time can be controlled with the temperature of water used

38
Q

What are 4 disadvantages of alginate

A

Poor dimensional stability
Incompatibility with some dental stones
Setting time is very dependent on operator handling
Needs to be kept damp or dries out

39
Q

What is the setting reaction equations for alginate

A

3Ca2+ + 2Na3PO4 = Ca3 (PO4)2 + 6NA+

40
Q

What happens in the setting reaction of alginate

A

Trisodium phosphate reacts with calcium sulphate until used up producing calcium phosphate and maintaining sol state then the calcium ions can react with sodium alginate

41
Q

What is the pH of alginate in a setting reaction

A

pH 11 to pH 7

42
Q

What happens to setting time when temperature is increased

A

Reduces setting time by increasing the uptake of Trisodium phosphate and increasing the rate of cross linkage formation

MCQ 1.2 (34 decks)

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